CTL-1 using the LRA instruction
Why do we receive a 000001 system error message (CTL-1) when we use the LRA instruction on a 7 GB system, but the LRA instruction works fine on a 2 GB system?
If an LRA is issued in 31-bit mode then a special operation exception will occur if the real address is above the 2 GB bar and the caller is in 31-bit mode.
A SAM64 needs to be issued before the LRA is called. On a 7 GB test system most of the real storage comes from above the 2 GB bar while on the 2 GB system the storage is below the bar. That is why this problem will only be seen on the 7 GB test system. If a customer needs storage whose real address is below the 2 GB bar then common blocks should be used.
For more information read the z/Architecture Principles of Operations.